Damn! Average 9 batteries against the SAC... Hell of a fight!

To shoot down a heavy bomber (in my opinion) it is neccesary to kill all engines from one side or kill the crew, or damage the fuel tanks. That's why recomendations are to use 3 missiles salvo, which they didn't do everytime. Also the old SA-2 missiles warhead radiofuse "Shmel" is not so effective as 5E11 and 5X49 on V-755 and 759 missiles.
Anyway, NVA crews are good, they allmost took SR-71, which Quadafy PVO didn't (even with better version of SA-2). So they did their best.